Rotating sputter magnetron assembly

ABSTRACT

A magnetron especially advantageous for low-pressure plasma sputtering or sustained self-sputtering having reduced area but full target coverage. The magnetron includes an outer pole face surrounding an inner pole face with a gap therebetween. The outer pole of the magnetron of the invention is smaller than that of a circular magnetron similarly extending from the center to the periphery of the target. Different shapes include a racetrack, an ellipse, an egg shape, a triangle, and a triangle with an arc conforming to the target periphery. The small shape allows high power densities to be applied to the area of the target actually being sputtered. Preferably, the magnetic flux produced by the outer pole is greater than that produced by the inner pole. The asymmetry provides several advantages in high-density plasma sputtering. The invention allows sustained self-sputtering of copper and allows sputtering of aluminum, titanium, and other metal at reduced pressures down to at least 0.1 milliTorr. However, at least for titanium, bottom coverage is improved for higher chamber pressures. For some metals, the pedestal bearing the wafer should be RF biased to a limited degree. The invention allows ionization fractions of the metal of 20% and greater with only the use of capacitive power coupling and can produce bottom coverage of greater than 25% in a hole having an aspect ratio of 5.

RELATED APPLICATION

This application is a continuation in part of Ser. No. 09/249,468, filedFeb. 12, 1999.

FIELD OF THE INVENTION

The invention relates generally to sputtering of materials. Inparticular, the invention relates to the magnetron creating a magneticfield to enhance sputtering.

BACKGROUND ART

Sputtering, alternatively called physical vapor deposition (PVD), is themost prevalent method of depositing layers of metals and relatedmaterials in the fabrication of semiconductor integrated circuits. Aconventional PVD reactor 10 is illustrated schematically in crosssection in FIG. 1, and the illustration is based upon the Endura PVDReactor available from Applied Materials, Inc. of Santa Clara, Calif.The reactor 10 includes a vacuum chamber 12 sealed to a PVD target 14composed of the material, usually a metal, to be sputter deposited on awafer 16 held on a heater pedestal 18. A shield 20 held within thechamber protects the chamber wall 12 from the sputtered material andprovides the anode grounding plane. A selectable DC power supply 22negatively biases the target 14 to about −600 VDC with respect to theshield 20. Conventionally, the pedestal 18 and hence the wafer 16 areleft electrically floating.

A gas source 24 supplies a sputtering working gas, typically thechemically inactive gas argon, to the chamber 12 through a mass flowcontroller 26. In reactive metallic nitride sputtering, for example, oftitanium nitride, nitrogen is supplied from another gas source 27through its own mass flow controller 26. Oxygen can also be supplied toproduce oxides such as Al₂O₃. The gases can be admitted to the top ofthe chamber, as illustrated, or at its bottom, either with one or moreinlet pipes penetrating the bottom of the shield or through the gapbetween the shield 20 and the pedestal 18. A vacuum system 28 maintainsthe chamber at a low pressure. Although the base pressure can be held toabout 10⁻⁷ Torr or even lower, the pressure of the working gas istypically maintained at between about 1 and 1000 mTorr. A computer-basedcontroller 30 controls the reactor including the DC power supply 22 andthe mass flow controllers 26.

When the argon is admitted into the chamber, the DC voltage between thetarget 14 and the shield 20 ignites the argon into a plasma, and thepositively charged argon ions are attracted to the negatively chargedtarget 14. The ions strike the target 14 at a substantial energy andcause target atoms or atomic clusters to be sputtered from the target14. Some of the target particles strike the wafer 16 and are therebydeposited on it, thereby forming a film of the target material. Inreactive sputtering of a metallic nitride, nitrogen is additionallyadmitted into the chamber 12, and it reacts with the sputtered metallicatoms to form a metallic nitride on the wafer 16.

To provide efficient sputtering, a magnetron 32 is positioned in back ofthe target 14. It has opposed magnets 34, 36 creating a magnetic fieldwithin the chamber in the neighborhood of the magnets 34, 36. Themagnetic field traps electrons and, for charge neutrality, the iondensity also increases to form a high-density plasma region 38 withinthe chamber adjacent to the magnetron 32. The magnetron 32 is usuallyrotated about the center of the target 14 to achieve full coverage insputtering of the target 14. The form of the magnetron is a subject ofthis patent application, and the illustrated form is intended to be onlysuggestive.

The advancing level of integration in semiconductor integrated circuitshas placed increasing demands upon sputtering equipment and processes.Many of the problems are associated with contact and via holes. Asillustrated in the cross-sectional view of FIG. 2, via or contact holes40 are etched through an interlevel dielectric layer 42 to reach aconductive feature 44 in the underlying layer or substrate 46.Sputtering is then used to fill metal into the hole 40 to provideinter-level electrical connections. If the underlying layer 46 is thesemiconductor substrate, the filled hole 40 is called a contact; if theunderlying layer is a lower-level metallization level, the filled hole40 is called a via. For simplicity, we will refer hereafter only tovias. The widths of inter-level vias have decreased to the neighborhoodof 0.25 μm and below while the thickness of the inter-level dielectrichas remained nearly constant at around 0.7 μm. As a result, the viaholes in advanced integrated circuits have increased aspect ratios ofthree and greater. For some technologies under development, aspectratios of six and even greater are required.

Such high aspect ratios present a problem for sputtering because mostforms of sputtering are not strongly anisotropic, a cosine dependenceoff the vertical being typical, so that the initially sputtered materialpreferentially deposits at the top of the hole and may bridge it, thuspreventing the filling of the bottom of the hole and creating a void inthe via metal.

It has become known, however, that deep hole filling can be facilitatedby causing a significant fraction of the sputtered particles to beionized in the plasma between the target 14 and the pedestal 18. Thepedestal 18 of FIG. 1, even if it is left electrically floating,develops a DC self-bias, which attracts ionized sputtered particles fromthe plasma across the plasma sheath adjacent to the pedestal 18 and deepinto the hole 40 in the dielectric layer 42. The effect can beaccentuated with additional DC or RF biasing of the pedestal electrode18 to additionally accelerate the ionized particles extracted across theplasma sheath towards the wafer 16, thereby controlling thedirectionality of sputter deposition. The process of sputtering with asignificant fraction of ionized sputtered atoms is called ionized metaldeposition or ionized metal plating (IMP). Two related quantitativemeasures of the effectiveness of hole filling are bottom coverage andside coverage. As illustrated schematically in FIG. 2, the initial phaseof sputtering deposits a layer 50, which has a surface or blanketthickness of s₁, a bottom thickness of s₂, and a sidewall thickness ofs₃. The bottom coverage is equal to s₂/s₁, and the sidewall coverage isequal to s₃/s₁. The model is overly simplified but in many situations isadequate.

One method of increasing the ionization fraction is to create ahigh-density plasma (HDP), such as by adding an RF coil around the sidesof the chamber 12 of FIG. 1. An HDP reactor not only creates ahigh-density argon plasma but also increases the ionization fraction ofthe sputtered atoms. However, HDP PVD reactors are new and relativelyexpensive, and the quality of the deposited films is not always thebest. It is desired to continue using the principally DC sputtering ofthe PVD reactor of FIG. 1.

Another method for increasing the ionization ratio is to use ahollow-cathode magnetron in which the target has the shape of a top hat.This type of reactor, though, runs very hot and the complexly shapedtargets are very expensive.

It has been observed that copper sputtered with either an inductivelycoupled HDP sputter reactor or a hollow-cathode reactor tends to form anundulatory copper film on the via sidewall, and further the depositedmetal tends to dewet. The variable thickness is particularly seriouswhen the sputtered copper layer is being used as a seed layer of apredetermined minimum thickness for a subsequent deposition process suchas electroplating to complete the copper hole filling.

A further problem in the prior art is that the sidewall coverage tendsto be asymmetric with the side facing the center of the target beingmore heavily coated than the more shielded side facing a larger solidangle outside the target. Not only does the asymmetry require excessivedeposition to achieve a seed layer of predetermined minimum thickness,it causes cross-shaped trenches used as alignment indicia in thephotolithography to appear to move as the trenches are asymmetricallynarrowed.

Another operational control that promotes deep hole filling is chamberpressure. It is generally believed that lower chamber pressures promotehole filling. At higher pressures, there is a higher probability thatsputtered particles, whether neutral or ionized, will collide with atomsof the argon carrier gas. Collisions tend to neutralize ions and torandomize velocities, both effects degrading hole filling. However, asdescribed before, the sputtering relies upon the existence of a plasmaat least adjacent to the target. If the pressure is reduced too much,the plasma collapses, although the minimum pressure is dependent uponseveral factors.

The extreme of low-pressure plasma sputtering is sustainedself-sputtering (SSS), as disclosed by Fu et al. in U.S. patentapplication Ser. No. 08/854,008, filed May 8, 1997. In SSS, the densityof positively ionized sputtered atoms is so high that a sufficientnumber are attracted back to the negatively biased target to resputtermore ionized atoms. Under the right conditions for a limited number oftarget metals, the self-sputtering sustains the plasma, and no argonworking gas is required. Copper is the metal most prone to SSS, but onlyunder conditions of high power and high magnetic field. Coppersputtering is being seriously developed because of copper's lowresistivity and low susceptibility to electromigration. However, forcopper SSS to become commercially feasible, a full-coverage, high-fieldmagnetron needs to be developed.

Increased power applied to the target allows reduced pressure, perhapsto the point of sustained self-sputtering. The increased power alsoincreases the ionization density. However, excessive power requiresexpensive power supplies and increased cooling. Power levels in excessof 20 to 30 kW are considered infeasible in a commercial environment. Infact, the pertinent factor is not power but the power density in thearea below the magnetron since that is the area of the high-densityplasma promoting effective sputtering. Hence, a small, high-field magnetwould most easily produce a high ionization density. For this reason,some prior art discloses a small circularly shaped magnet. However, sucha magnetron requires not only rotation about the center of the target toprovide uniformity, but it also requires radial scanning to assure fulland fairly uniform coverage of the target. If full magnetron coverage isnot achieved, not only is the target not efficiently used, but moreimportantly the uniformity of sputter deposition is degraded, and someof the sputtered material redeposits on the target in areas that are notbeing sputtered. Furthermore, the material redeposited on unsputteredareas may build up to such a thickness that it is prone to flake off,producing severe particle problems. While radial scanning canpotentially avoid these problems, the required scanning mechanisms arecomplex and generally considered infeasible in a production environment.

One type of commercially available magnetron is kidney-shaped, asexemplified by Tepman in U.S. Pat. No. 5,320,728. Parker discloses moreexaggerated forms of this shape in U.S. Pat. No. 5,242,566. Asillustrated in plan view in FIG. 3, the Tepman magnetron 52 is based ona kidney shape for the magnetically opposed pole faces 54, 56 separatedby a circuitous gap 57 of nearly constant width. The pole faces 54, 56are magnetically coupled by unillustrated horseshoe magnets bridging thegap 57. The magnetron rotates about a rotational axis 58 at the centerof the target 14 and near the concave edge of the kidney-shaped innerpole face 54. The convexly curved outer periphery of the outer pole face56, which is generally parallel to the gap 57 in that area, is close tothe outer periphery of the usable portion if the target 14. This shapehas been optimized for high field and for uniform sputtering but has anarea that is nearly half that of the target. It is noted that themagnetic field is relatively weak in areas separated from the pole gap57.

For these reasons, it is desirable to develop a small, high-fieldmagnetron providing full coverage so as to promote deep hole filling andsustained copper self-sputtering.

SUMMARY OF THE INVENTION

The invention includes a sputtering magnetron having an oval or relatedshape of smaller area than a circle of equal diameter where the twodiameters extend along the target radius with respect to the typicalrotation axis of the magnetron. The shapes include racetracks, ellipses,egg shapes, triangles, and arced triangles asymmetrically positionedabout the target center. The magnetron is rotated on the backside of thetarget about a point preferably near the magnetron's thin end, and thethicker end is positioned more closely to the target periphery.Preferably, the total magnetic flux is greater outside than inside thehalf radius of the target.

The small area allows an electrical power density of at least 600 W/cm²to be applied from an 18 kW power supply to a fully covered sputteringtarget used to sputter deposit a 200 mm wafer.

The magnetron is configured to produce less magnetic flux in its innerpole than in its surrounding outer pole. Thereby, the magnetic fieldreaches further into the sputtering chamber to promote low-pressuresputtering and sustained self-sputtering.

The invention also includes sputtering methods achievable with such amagnetron. The high magnetic field extending over a small closed areafacilitates sustained self-sputtering. Many metals not subject tosustained self-sputtering can be sputtered at chamber pressures of lessthan 0.5 milliTorr, often less than 0.2 milliTorr, and even at 0.1milliTorr. The bottom coverage can be further improved by applying an RFbias of less than 250 W to a pedestal electrode sized to support a 200mm wafer. Copper can be sputtered with 18 kW of DC power for a 330 mmtarget and 200 mm wafer either in a fully self-sustained mode or with aminimal chamber pressure of 0.3 milliTorr or less.

The invention provides for high-power density sputtering with powersupplies of reduced capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a DC plasma sputtering reactor.

FIG. 2 is a cross-sectional view of a inter-level via in a semiconductorintegrated circuit.

FIG. 3 is a plan view of a conventional magnetron.

FIG. 4 is a plan view of the pole pieces of an embodiment of themagnetron of the invention taken along the view line 4-4 of FIG. 7.

FIG. 5 is a plan view of the magnets used in the magnetron of FIG. 4.

FIG. 6 is a cross-sectional view of one of the magnets used inconjunction with the embodiments of the invention.

FIG. 7 is a cross-sectional view of the magnetron of FIG. 4.

FIG. 8 is a plan view of an egg-shaped magnetron.

FIG. 9 is a plan view of a triangularly shaped magnetron.

FIG. 10 is a plan view of a modification of the triangularly shapedmagnetron of FIG. 9, referred to as an arced triangular magnetron.

FIG. 11 is a plan view of the magnets used in the arced triangularmagnetron of FIG. 10.

FIG. 12 is a plan view of two model magnetrons used to calculate areasand peripheral lengths.

FIG. 13 is a graph of the angular dependences of the areas of atriangular and of a circular magnetron.

FIG. 14 is a graph of the angular dependences of the peripheral lengthsof the two types of magnetrons of FIG. 12.

FIG. 15 is a side view of an idealization of the magnetic field producedwith the described embodiments of the invention.

FIG. 16 is a graph showing the effect of RF wafer bias in bottomcoverage in titanium sputtering.

FIG. 17 is a graph of the dependence of chamber pressure upon nitrogenflow illustrating the two modes of deposition obtained in reactivesputtering of titanium nitride with a magnetron of the invention.

FIG. 18 is a graph of the step coverage obtained in the two sputteringmodes for reactive sputtering of titanium nitride with a magnetron ofthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the invention is a racetrack magnetron 60, illustratedin plan view in FIG. 4. The racetrack magnetron 60 has a centralbar-shaped pole face 62 of one magnetic polarity having opposed parallelmiddle straight sides 64 connected by two rounded ends 66. The central,bar-shaped pole face 62 is surrounded by an outer elongated ring-shapedpole face 68 of the other polarity with a gap 70 of nearly constantwidth separating the bar-shaped and ring-shaped pole faces 62, 68. Theouter pole face 68 of the other magnetic polarity includes opposedparallel middle straight sections 72 connected by two rounded ends 74 ingeneral central symmetry with the inner pole face 62. The middlesections 72 and rounded ends 74 are bands having nearly equal widths.Magnets, to be described shortly, cause the pole faces 62, 68 to haveopposed magnetic polarities. A backing plate, also to be describedshortly, provides both a magnetic yoke between the magnetically opposedpole faces 62, 68 and support for the magnetron structure.

Although the two pole faces 62, 68 are illustrated with specificmagnetic polarities producing magnetic fields extending generallyperpendicularly to the plane of illustration, it is of courseappreciated that the opposite set of magnetic polarities will producethe same general magnetic effects as far as the invention is concerned.The illustrated assembly produces a generally semi-toroidal magneticfield having parallel arcs extending perpendicularly to a closed pathwith a minimal field-free region in the center. There results a closedtunnel of magnetic field forming struts of the tunnel.

The pole assembly of FIG. 4 is intended to be continuously rotatedduring sputter deposition at a fairly high rotation rate about arotation axis 78 approximately coincident with the center of the target14 of uniform composition. The rotation axis 78 is located at or nearone prolate end 80 of the outer pole face 68 and with its other prolateend 82 located approximately at the outer radial usable extent of thetarget 14. The asymmetric placement of the rotating magnetron 60 withrespect to the target center provides a small magnetron nonethelessachieving full target coverage. The outer usable periphery of the targetis not easily defined because different magnetron designs use differentportions of the same target. However, it is bounded by the flat area ofthe target and almost always extends to significantly beyond thediameter of the wafer being sputter deposited and is somewhat less thanthe area of the target face. For 200 mm wafers, target faces of 325 mmare typical. A 15% unused target radius may be considered as an upperpractical limit. Racetrack magnetrons are well known in the prior art,but they are generally positioned symmetrically about the center of thetarget. In the described invention, the racetrack is asymmetricallypositioned with its inner end either overlying the target center orterminating at a radial position preferably within 20% and morepreferably within 10% of the target radius from the target center. Theillustrated racetrack extends along a diameter of the target.

As illustrated in the plan view of FIG. 5, two sets of magnets 90, 92are disposed in back of the pole faces 62, 68 to produce the twomagnetic polarities. The combination of the pole faces 62, 68, themagnets 90, 92, and possibly a back magnetic yoke produces two oppositemagnetic poles having areas defined by the pole faces 62, 68. Othermeans may be used to achieved such poles.

The two types of magnets 90, 92 may be of similar construction andcomposition producing an axially extending magnetic flux on eachvertically facing end. If they are of different, magnetic composition,diameter, or length, the flux produced by different magnets may bedifferent. A cross-sectional view of a magnet 90, 92 is shown in FIG. 6.A cylindrical magnetic core 93 extending along an axis is composed of astrongly magnetic material, such as neodymium boron iron (NdBFe).Because such a material is easily oxidized, the core 93 is encapsulatedin a case made of a tubular sidewall 94 and two generally circular caps96 welded together to form an air-tight canister. The caps 96 arecomposed of a soft magnetic material, preferably SS410 stainless steel,and the tubular sidewall 94 is composed of a non-magnetic material,preferably SS304 stainless steel. Each cap 96 includes an axiallyextending pin 97, which engages a corresponding capture hole in one ofthe pole faces 62, 68 or in a magnetic yoke to be shortly described.Thereby, the magnets 90, 92 are fixed in the magnetron. The magneticcore 93 is magnetized along its axial direction, but the two differenttypes of magnets 90, 92 are oriented in the magnetron 60, as illustratedin the cross-sectional view of FIG. 7, so that the magnets 90 of theinner pole 62 are aligned to have their magnetic field extendingvertically in one direction, and the magnets 92 of the outer pole 68 arealigned to have their magnetic field extending vertically in the otherdirection. That is, they have opposed magnetic polarities.

As illustrated in the cross-sectional view of FIG. 7, the magnets 90, 92are arranged closely above (using the orientation of FIG. 1) the polefaces 62, 68 located just above the back of the target 14. A magneticyoke 98 having a generally closed shape generally conforming to theouter periphery of the outer pole face 68 is closely positioned in backof the magnets 90, 92 to magnetically couple the two poles 62, 68. Asmentioned previously, holes in the pole faces 62, 68 and in the yoke 98fix the magnets 90, 92, and unillustrated hardware fix the pole faces62, 68 to the yoke 98.

The inner magnets 90 and inner pole face 62 constitute an inner pole ofone magnetic polarity while the outer magnets 92 and the outer pole face68 constitute a surrounding outer pole of the other magnetic polarity.The magnetic yoke 98 magnetically couples the inner and outer poles andsubstantially confines the magnetic field on the back or top side of themagnetron to the yoke 98. A semi-toroidal magnetic field 100 is therebyproduced, which extends through the non-magnetic target 14 into thevacuum chamber 12 to define the high-density plasma region 38. The field100 extends through the non-magnetic target 14 into the vacuum chamber12 to define the extent of the high-density plasma region 38. Themagnets 90, 92 may be of different magnetic strength. However, it isdesired for reasons to be explained later that the total magnetic fluxproduced by the outer magnets 92 be substantially greater than thatproduced by the inner magnets 90. As illustrated, the magnetron 60extends horizontally from approximately the center of the target 14 tothe edge of the usable area of the target 14. The magnetic yoke 90 andthe two pole faces 62, 68 are preferably plates formed of a softmagnetic material such as SS416 stainless steel.

The inner prolate end 80 of the magnetron 60 is connected to a shaft 104extending along the rotation axis 78 and rotated by a motor 106. Asillustrated, the magnetron 60 extends horizontally from approximatelythe center of the target 14 to the right hand side of the usable area ofthe target 14. Demaray et al. in U.S. Pat. No. 5,252,194 discloseexemplary details of the connections between the motor 106, themagnetron 60, and the vacuum chamber 12. The magnetron assembly 60should include counter-weighting to avoid flexing of the shaft 104.Although the center of rotation 78 is preferably disposed within theinner prolate end 74 of the outer pole face 72, its position may beoptimized to a slightly different position, but one preferably notdeviating more than 20%, more preferably 10%, from the inner prolate end80 as normalized to the prolate length of the magnetron 60. Mostpreferably, the inner end of the outer pole face 68 near the prolate end80 overlies the rotation center 78.

The racetrack configuration of FIG. 4 has the advantage of simplicityand a very small area while still providing full target coverage. Aswill be discussed later, the asymmetric magnetic flux of the two polesis advantageous for low-pressure sputtering and sustainedself-sputtering.

The racetrack configuration of FIG. 4 can be alternatively characterizedas an extremely flattened oval. Other oval shapes are also includedwithin the invention, for example, continuously curved shapes ofcontinuously changing diameter such as elliptical shapes with the majoraxis of the ellipse extending along the radius of the target and withthe minor axis preferably parallel to a rotational circumference.Tabuchi illustrates a symmetric oval magnetron in Laid-open JapanesePatent Application 63-282263. This shape however has the disadvantage ofa complex shape, especially for packing the magnets in the inner pole.

Another oval shape is represented by an egg-shaped magnetron 106,illustrated in plan view in FIG. 8. It has an outer pole face 108 of onemagnetic polarity surrounding an inner pole face 110 of the otherpolarity with a nearly constant gap 122 between them. Both pole faces108, 110 are shaped like the outline of an egg with a major axisextending along the radius of the target. However, an inner end 112 ofthe outer pole face 108 near the rotation axis 78 is sharper than anouter end 114 near the periphery of the target. The egg shape is relatedto an elliptical shape but is asymmetric with respect to the targetradius. Specifically, the minor axis is pushed closer to the targetperiphery than its center. The inner pole face 110 and the gap 122 aresimilarly shaped. Such an egg shape places more of the magnetic fluxcloser to the target periphery so as to improve sputtering uniformity.Such a preferred flux distribution may be characterized with respect tothe half radius of the target extending from its center to its outerusable radius. For improved uniformity, the total magnetic flux locatedoutside the half radius is greater than that located inside the halfradius, for example, by at least a 3:2 ratio, and preferably between 1.8and 2.3. The ratio of magnetic flux outside to inside the target halfradius in this configuration is about 2:1.

A related shape is represented by a triangular magnetron 126,illustrated in plan view in FIG. 9. It has a triangular outer pole face128 of one magnetic polarity surrounding a substantially solid innerpole face 130 of the other magnetic polarity with a gap 132 betweenthem. The triangular shape of the inner pole face 130 with roundedcorners allows hexagonal close packing of the button magnets 90, 92 ofFIG. 6. The outer pole face 128 has three straight sections 134 arepreferably offset by 60° with respect to each other and are connected byrounded corners 136. Preferably, the rounded corners 136 have smallerlengths than the straight sections 134. One rounded corner 136 islocated near the rotation center 78 and target center, preferably within20%, more preferably within 10% of the target radius, and mostpreferably with the apex portion of the outer pole face 128 overlyingthe rotation center 78. The triangularly shaped inner pole piece 130 mayinclude a central aperture, but it is preferred that the size of such anaperture be kept small to minimize the size of the central magneticcusp.

A modified triangular shape is represented by an arced triangularmagnetron 140 of FIG. 10. It includes the triangular inner pole face 130surrounded by an arced triangular outer pole face 142 with a gap 144between them and between the magnets of the respective poles and withthe magnetic yoke in back of the gap 144. The outer pole face 142includes two straight sections 146 connected to each other by a roundedapex corner 148 and connected to an arc section 150 by roundedcircumferential corners 152. The apex corner 148 is placed near therotational center 78 and the target center, preferably within 20% andmore preferably within 10% of the target radius. The arc section 150 islocated generally near the circumferential periphery of the target. Itscurvature may be equal to that of the target, that is, be equidistantfrom the center of rotation 78, but other optimized curvatures may bechosen for an arc section concave with respect to the rotational center78. It is located near the target periphery within the chamber,preferably within 25% and more preferably within 15% of the radius tothe periphery. Yokoyama et al. in Laid-open Japanese Patent Application62-89864 discloses the advantage of a plurality of arced triangularmagnetrons arranged symmetrically about the target center. However,plural magnetrons do not provide for a small total area and thus do notachieve a high power density for sputtering. Furthermore, the apices ofthe individual magnetron sections in Yokoyama are located relatively farfrom the target center, thus producing poor sputtering uniformity exceptfor a large number of sections.

The magnetic field is produced by an arrangement of magnets shown inplan view in FIG. 11. Magnets 160 of a first polarity are disposedadjacent to the inner pole face 130 in an advantageous hexagonallyclose-packed arrangement. Magnets 162 of a second polarity are arrangedadjacent to the arc section 150 of the outer pole face 142 while magnets164 of the second polarity are arranged adjacent to the remainingportions of the outer pole face 142. In some situations, to be describedlater, it is advantageous to place magnets of different intensities atdifferent portions of the outer pole face 142. In one embodiment, thereare 10 magnets in the inner pole and 25 magnets in the outer pole, whichfor magnets of equal strength produces 2.6 more magnetic flux in theouter pole than in the inner pole.

The triangular magnetrons 126, 140 of FIGS. 9 and 10 are illustrated ashaving apex angles θ of 60°, which facilitates promotes hexagonal closepacking of the button magnets, but the apex angle can be changed, inparticular decreased below 60°. However, 60°±15° seems to providesuperior uniformity. The apex angle significantly affects two importantparameters of the magnetron of the invention, the values of its area Aand its perimeter P. Some simple calculations, most easily done for thearced triangular magnetron 140, show the general effects of changing theapex angle θ, as illustrated in plan view in FIG. 12. A simplified ormodel arced triangular magnetron 170 has two straight sides extendingbetween the center and periphery of the target 14 of radius R_(T) andmeeting at an apex coincident with the rotation axis 78 and furtherincludes an arc side conforming to the usable periphery of the target14. The area A of the simplified arced triangular magnetron 170 isθR_(T) ²/2, and its periphery P is R_(T)(2+θ), where θ is measured inradians. Also illustrated in FIG. 12 is a model circular magnetron 172having a radius of R_(T)/2 and having a diameter fixed to the rotationaxis 78. It has an area A of πR_(T) ²/4 and a periphery P of πR_(T).Both magnetrons 170, 172 provide full target coverage. The dependence ofthe arced triangular area A upon the apex angle θ is plotted innormalized units in FIG. 13 by line 174 and that for the circular areaby line 176. Below 90°, the triangular area is smaller. The dependenceof the triangular periphery P is plotted in FIG. 14 by line 178 and thatfor the circular periphery by line 180. Below 65.4°, the arcedtriangular periphery is smaller. Ionization efficiency is increased byminimizing the area, since the target power is concentrated in a smallerarea, and is also increased by minimizing the periphery, since edge lossis generally proportional to the peripheral length. Of course, the areaneeds to be large enough to accommodate the magnets creating themagnetic field. Also, these calculations do not address uniformity. Itis likely that the circular magnetron 170 provides reduced uniformityrelative to the arced triangular magnetron 172.

The ratio of the magnetic flux outside to inside the target half radiusfor the arced triangular magnetron 172 can be approximated by thelengths of the sides 170 in the two regions by (1+θ), which is 1.79 foran apex angle θ of 45°, 2.05 for 60°, 2.31 for 75°, and 2.57 for 90°.

A variation of the arced triangular arrangement of FIGS. 10 and 11decreases the apex angle to, for example, 47°. In addition to thehexagonally close packed inner magnets 160, one or more inner magnetsare linearly arranged from the inner corner of hexagonally closed packedmagnets toward the inner corner of the outer magnets 164. The result isintermediate the racetrack magnetron and the arced triangular magnetron.

It is understood that the shapes described above refer to pole faceshaving band-like widths of area not significantly larger than the buttonmagnets being used. The widths, particularly of the outer pole face, canbe increased, perhaps even non-uniformly, but the additional width is ofless effectiveness in generating the desired high magnetic field.

The shapes presented above have all been symmetric about the targetradius. However, the magnetron of the invention includes not only shapesasymmetric about the target center but also asymmetric about the targetradius, for example one radially extending side being in the form of theracetrack of FIG. 4 and the other side being oval, e.g., the egg shapeof FIG. 7, or one radially extending side being oval or straight and theother side having a triangular apex between the center and periphery ofthe target.

All the magnetrons described above have asymmetric areas for the innerand outer poles and, assuming similar packing of similar button magnets90, 92, asymmetric magnetic flux. In particular, the total magnetic flux∫B·dS produced by the inner pole 190, illustrated schematically in FIG.15, is much less than that produced by the surrounding outer pole 192,for example, by at least a factor of 1.5 and preferably 2. All themagnetrons are also characterized as having a compact inner pole 190surrounded by the outer pole 192. The result is a magnetic fielddistribution which is very strong in the reactor processing area 194adjacent to the gap 196 between the poles 190, 192, but which alsoextends far into the processing area 194 as the magnetic field lines ofthe outer pole 192 close back to the magnetic yoke 198. The substantialfraction of magnetic field extending vertically from the target deepinto the processing area 194 offers many advantages. Because the lightelectrons orbit around magnetic field lines, the extended magnetic fieldtraps electrons and thus helps to support a higher-density plasma deepinto the processing area 194. By the same interaction, the magneticfield extending close and parallel to the grounded chamber shieldreduces electron loss to the shield, also increasing the density of theplasma. As a result, the plasma can be supported at lower pressure oreven be self-sustained. The magnetic field also partially traps heavierpositive particles and thus guides ionized sputtered particles towardsthe wafer.

The inventive magnet also achieves a relatively high magnetic field.However, magnetic field intensity of itself is insufficient. Someconventional magnetrons, such as Demaray et al. disclose in theaforecited patent, use a line of horseshoe magnets arranged in akidney-shaped linear path with only a small gap between the poles of thehorseshoes. As a result, a relatively high magnetic field intensity canbe achieved in the area at the periphery of the kidney shape. However,the linear shape of the high magnetic field surrounds an area ofsubstantially no magnetic field. As a result, electrons can escape tonot only the exterior but also the interior of the high-field region. Incontrast, the inner pole of the triangular magnetron of the inventionproduces a magnetic cusp of minimal area. If electrons are lost from themagnetic field on one side of the inner pole, they are likely to becaptured on the other side, thus increasing the plasma density for agiven power level. Furthermore, the inner pole includes a singlemagnetizable pole face producing a generally uniform magnetic flux. Ifmultiple inner poles faces were used for multiple inner magnets,magnetic field lines would extend to between the inner magnets.

A further advantage of the inventive design is that one pole is formedin a closed line and surrounds the other pole. It would be possible toform a very small linearly extending magnetron with high magnetic fieldintensity by arranging horseshoe magnets or the like in an open endedline with the two sets of poles being closely spaced. However, theelectrons could then easily escape from the open ends and decrease thedensity of the plasma.

It is believed that the beneficial results of the invention are achievedin large part because the oval magnetrons and magnetrons of relatedshapes produce a higher plasma ionization density without requiringexcessive power. Nonetheless, full target coverage is achieved. In oneaspect, the inventive magnetron has a relatively small area, but has ashape that allows full target coverage without radial scanning. Thetriangular magnetron 160 of FIG. 10 with an apex angle of 60° has anarea of ⅙ (0.166) of the usable target area. In contrast, if thecircular magnetron 162 were used, which similarly extends from thetarget center to the periphery, the magnetron area is ¼ (0.25) of thetarget area. As a result, the power density is less for a given powersupply powering a larger circular magnetron. The target overlaypercentage is even higher for the Tepman magnet of FIG. 3.

The combination of small area and full coverage is achieved by an outermagnetron shape extending from the target center to its usable periphery(±15%) and having a transverse dimension at half the target radius ofless substantially less than the target radius, that is, prolate alongthe target radius. The transverse dimension should be measuredcircumferentially along the rotation path.

The uniformity is enhanced by an oval shape that is transversely wider,with respect to the target radius, at its outer end near the targetperiphery than at its inner end near the center of rotation. That is,the minor axis is displaced towards the target circumference.

The small area of the magnetron, but nonetheless providing full targetcoverage, allows a very high power density to be applied to the targetwith a reasonably sized power supply. The small area, unlike the Tepmandesign, has no substantial field-free region included in its interior.Some of the examples below use an 18 kW power source. For a 200 mmwafer, the magnetron extends out to a usable target diameter of about300 mm. The effective area of the arced triangular magnetron is aboutone-sixth of the area associated with this larger diameter, that is,about 117 cm². Thus, the average power density of the area beingsputtered at any given location of the magnetron is about 150 W/cm².Such a high power density achieved without inductive coils can support aplasma at lower argon pressure or permit sustained self-sputtering forselected metals such as copper. Even with 300 mm wafers, a 27 kW powersupply in conjunction with the small magnetron of the invention scaledto the larger dimension will produce a target power density of 103W/cm². As shown below, a power density of 76 W/cm² is sufficient forsustained self-sputtering of copper.

Processes

A racetrack magnetron of FIGS. 4 and 5 was tested with coppersputtering. In one configuration, six magnets 90 are placed behind thecenter pole face 62, twenty-five magnets of the same strength butopposite polarity are arranged behind and around the outer pole face 68,and the spacing between the 33 cm target and the 200 mm wafer is 190 mm.This configuration produces a deposition uniformity of ±18%. In a secondconfiguration, the magnets have different strengths, the stronger onesproducing 30% more magnetic flux. Six strong magnets are placed behindthe center pole face, and 24 weaker magnets are placed around the outerpole face. Despite the stronger inner magnets, the total magnetic fluxproduced by the outer magnets is greater than that produced by the innerones. The second configuration produces an improved depositionuniformity of 8.9%. The second configuration also produces superior holefilling into a 0.5 μm-wide, 2 μm-deep via hole. For 265 nm of blanketcopper, the bottom coverage is between 10 and 15%, and the sidewallcoverage is about 2.8%. The deep hole filling is promoted by the smallarea of the racetrack magnetron producing a higher ionization density.In a third configuration, strong magnets replace some of the weakermagnets near the ends of the outer pole. This produces a somewhat betteruniformity.

An arced triangular magnetron of FIGS. 10 and 11 was tested in a seriesof experiments with different sputtering composition. For almost all theexperiments, the target was spaced between 190 and 200 mm from the waferand the target had a diameter of 330 mm for a 200 mm wafer.

Copper

For copper sputtering, uniformity is improved by using ten strongmagnets 160 in the inner pole, strong magnets 162 along the arc portion150 of the outer pole, and weaker magnets 164 for the remainder of theouter pole. The stronger magnets have a diameter 30% larger than thediameter of the weaker magnets, but are otherwise of similar compositionand structure, thereby creating an integrated magnetic flux that is 70%larger.

Sustained self-sputtering of copper is achieved, after striking theplasma in an argon ambient, with 9 kW of DC power applied to the targethaving a usable diameter of about 30 cm, which results in a powerdensity of 76 W/cm² with the arced triangular magnetron. However, it isconsidered desirable to operate with 18 kW of DC power and with aminimal argon pressure of about 0.1 milliTorr arising at least in partfrom leakage of the gas providing backside cooling of the wafer to theliquid-chilled pedestal. The increased background pressure of 0.1 to 0.3milliTorr enhances effective wafer cooling without significant increasein the scattering and deionization of the sputtered ions. Theserelatively low DC powers are important in view of the ongoingdevelopment of equipment for 300 mm wafers, for which these numbersscale to 20 kW and 40 kW. A power supply of greater than 40 kW isconsidered expensive if not infeasible.

One application of ionized copper sputtering is to deposit a thinconformal seed layer of copper in a deep and narrow via hole.Thereafter, electro or electroless plating can be used to quickly andeconomically fill the remainder of the hole with copper.

In one experiment, a via hole having a top width of 0.30 μm andextending through 1.2 μm of silica was first coated with a Ta/TaNbarrier layer. Using the arced triangular magnetron, copper wasdeposited over the barrier layer at 18 kW of target power and a pressureof 0.2 milliTorr. The deposition was carried out to a blanket thicknessof about 0.15 μm. The sides of the via hole was smoothly covered. Theexperiments show that the sidewall thickness of the copper is about 7 nmon one side and 11.4 nm on the other side (5% and 8%) for a via locatedat the wafer edge. The bottom coverage is about 24 nm (16%). Sidewallsymmetry is improved for a via hole at the wafer center. The smoothnesspromotes the use of the deposited layer as a seed layer and as anelectrode for subsequent electroplating of copper. The relatively goodsymmetry between the two sidewalls relieves the problem in the prior artof apparently moving photolithographic indicia.

Aluminum

Using the arced triangular magnetron, sputtering of an aluminum targetwas achieved at both 12 kW and 18 kW of applied power with a minimumpressure of about 0.1 milliTorr, a significant improvement. For aluminumsputtering, sidewall coverage and particularly bottom coverage issignificantly improved. The better uniformity is also believed to berelated in part to the increased ionization fraction since theself-biased pedestal supporting the wafer attracts the ionized sputteredparticles across its entire area. It is estimated that the magnetron ofthe invention increases the ionization fraction from 2% to at least 20%and probably 25%.

The arced triangular magnetron was compared under similar operatingconditions to the operation of a conventional magnetron resembling theTepman magnetron of FIG. 3. The comparative results are summarized inTABLE 1 for the sputtering of aluminum.

TABLE 1 Triangle Conv. Bottom 28.5% 8.0% Coverage Sidewall 8.0% 5.7%Coverage Uniformity 4.6% 7.8% (190 mm) Uniformity 3.0% 6.0% (290 mm)Minimum 0.1 0.35 Pressure (milliTorr)

The coverage results were obtained for via holes having a width of 0.25μm and a depth of 1.2 μm, that is, an aspect ratio of about 5. Thebottom coverage is significantly improved with the inventive triangularmagnetron compared to the conventional magnetron. The sidewall coverageis also increased, and further the coverage is smooth and uniform fromtop to bottom. These two characteristics promote the use of thedeposited metal layer as a seed layer for a subsequent deposition step.This is particularly important for copper in which the second depositionis performed by a different process such as electroplating. Theincreased bottom and sidewall coverages are believed to be due to thehigher ionization fraction of sputtered aluminum atoms achieved with theinventive triangular magnetron. This ionization fraction is believed tobe 25% or greater. The uniformity of blanket (planar) deposition wasdetermined both for a separation of 190 mm between the target and thewafer and, in a long-throw implementation, for a separation of 290 mm.The inventive triangular magnetron produces better uniformity,especially for long throw. The better uniformity is also believed to berelated to the increased ionization fraction since the self-biasedpedestal supporting the wafer attracts the ionized sputtered particlesacross its entire area. Similarly, the inventive triangular magnetronproduces less asymmetry between the coverages of the two opposedsidewalls. The increased ionization density is due in part to therelatively small inner yoke having an area substantially less than thatof the outer yoke. As a result, electrons lost from one side of theinner yoke are likely to be captured by the other side.

Titanium

The arced triangular magnetron was also used to sputter titanium.Titanium, sometimes in conjunction with titanium nitride, is useful inaluminum metallization for providing a silicided contact to silicon atthe bottom of a contact hole and to act as wetting layer and inconjunction with a titanium nitride layer as a barrier both to thesilicon in a contact hole and between the aluminum and the silicadielectric on the via or contact sidewalls. Conformal and relativelythick coatings are thus required.

A series of experiments were performed using a titanium target with 18kW of DC target power and with only six magnets 160 in the inner pole.At a chamber pressure of 0.35 milliTorr, the bottom coverage anduniformity are observed to be good.

The titanium experiments were continued to measure bottom coverage as afunction of the aspect ratio (AR) of the via hole being coated. With nowafer bias applied and the pedestal heater 18 left electricallyfloating, the 18 kW of target power nonetheless self-biases the targetto about 30 to 45V. The bottom coverage under these conditions is shownby line 190 in the graph of FIG. 16. The bottom coverage decreases forholes of higher aspect ratios but is still an acceptable 20% at AR=6.

In a continuation of these experiments, an RF power source 192,illustrated in FIG. 1, was connected to the heater pedestal 18 through acoupling capacitor circuit 194. It is known that such an RF fieldapplied to the wafer adjacent to a plasma creates a DC self-bias. When100 W of 400 kHz power is applied with a chamber pressure of 0.3milliTorr, the bottom coverage is significantly increased, as shown byline 196 in the graph of FIG. 16. However, when the bias power isincreased to 250 W, resputtering and faceting of the top corners of thevia hole becomes a problem. The bottom coverage results for 250 W biasare shown by line 198. For aspect ratios above 4.5, the bottom coveragewith 250 W of wafer bias is generally worse than for 100 W of wafer biasso bias powers should be kept below 250 W for lower bias frequencies of2 MHz or less. These powers should be normalized to a 200 mm circularreference wafer. Other sizes of wafers, such as a 300 mm wafer can beused, and these wafers may not be completely circularly because ofindexing flats or notches. However, the same effects are expected whenthe power levels quoted above are referenced to a 200 mm circularreference wafer and then scaled according to the differing area of asubstantially circular working wafer.

The experiments were continued for holes with aspect ratios of 4.5 using300 W of RF wafer bias at a frequency of 13.56 MHz. At a pressure of 0.7milliTorr, the blanket deposition rate is 128 nm/min, and the bottomcoverage varies between 31% and 52%. At a pressure of 1.4 milliTorr, thedeposition rate is 142 nm/min, and the bottom coverage varies between42% and 62%. At the higher pressure, the sidewall coverage variesbetween 10.4% and 11.5%, and no appreciable sidewall asymmetry isobserved. Contrary to expectations, pressures above 0.7 milliTorrproduce higher titanium deposition rates and better bottom coverage. Thehigher bias frequency permits a higher bias power to be applied.

Titanium nitride

The magnetron of the invention can also be used for reactive sputtering,such as for TiN, in which nitrogen is additionally admitted into thechamber to react with the sputtered metal, for example, with titanium toproduce TiN or with tantalum to produce TaN. Reactive sputteringpresents a more complex and varied chemistry. Reactive sputtering toproduce TiN is known to operate in two modes, metallic mode and poisonmode. Metallic mode produces a high-density, gold-colored film on thewafer. Poison mode, which is often associated with a high nitrogen flow,produces a purple/brown film which advantageously has low stress.However, the poison-mode film has many grain boundaries, and filmdefects severely reduce chip yield. Furthermore, the deposition rate inpoison mode is typically only one-quarter of the rate in metallic mode.It is generally believed that in poison mode the nitrogen reacts withthe target to form a TiN surface on the Ti target while in metallic modethe target surface remains clean and TiN forms only on the wafer.

The arced triangular magnetron was tested for reactive sputtering oftitanium nitride in the same chamber used for sputter depositingtitanium.

The initialization conditions for sputter depositing titanium nitrideare found to be very important to obtain operation in the metallic mode.In a series of initial experiments, argon alone is first admitted to thechamber. After the plasma is struck at an argon pressure of about 0.5milliTorr, the argon flow is reduced to 5 sccm producing a pressure of0.3 milliTorr. When the nitrogen flow is then step wise ramped up to 100sccm and then is gradually reduced, the dependence of the chamberpressure upon the flow assumes a hysteretic form illustrated in FIG. 17.Between about 50 and 70 sccm of nitrogen, intermediate ramp-up pressures200 are below corresponding intermediate ramp-down pressures 202. Atlower pressures 204 and at higher pressures 206, there is no significantseparation between ramp up and ramp down. It is believed that the lowerpressures 204 and intermediate ramp-up pressures 200 cause sputtering inmetallic mode while higher pressures 206 and intermediate ramp-downpressures 202 cause sputtering in poison mode.

These results show that, for higher operational deposition rates in thegenerally preferred metallic mode, it is important to not exceed theintermediate ramp-up pressures 200, that is, not to exceed the maximummetallic-mode flow, which in these experiments is 70 sccm or slightlyhigher but definitely below 80 sccm. The argon and nitrogen can besimultaneously and quickly turned on, but preferably the DC power isalso quickly turned on.

There are some applications, however, where operation in poison mode ispreferred. This can be achieved by first going to the higher pressures206 and then decreasing to the ramp-down intermediate pressures 202.Alternatively, poison mode can be achieved by immediately turning on thedesired gas flow, but only gradually turning on the DC sputtering powersupply at a rate of no more than 5 kW/s.

Titanium nitride was sputtered into high aspect-ratio via holes in bothmetallic and poison modes at a N₂ flow of 50 sccm and an Ar flow of 5sccm after the plasma had been struck in argon. These flows produce apressure of 1.7 milliTorr in metallic mode and 2.1 milliTorr in poisonmode. The deposition rates are 100 nm/min in metallic mode and 30 nm/minin poison mode. On one hand, the TiN film stress is higher when it isdeposited in metallic mode, but on the other hand poison mode suffersfrom overhang and undulatory sidewall thicknesses near the top of thevia hole. A series of experiments deposited TiN into via holes ofdiffering aspect ratios. The resulting measured bottom coverage,illustrated in the graph of FIG. 18, shows in line 210 that bottomcoverage in metallic mode remains relatively high even with an viaaspect ratio of 5 while in line 212 the step coverage in poison mode isalways lower and drops dramatically for aspect ratios of four andhigher. However, when additionally the wafer is biased, step coverage ofTiN deposited in the poison mode is acceptable.

The success of depositing TiN in the same chamber used for depositing Tidemonstrates that the Ti/TiN barrier can be deposited according to theinvention in one continuous operation.

Integrated tungsten plug process

Two series of tests were performed to demonstrate an integrated processcombining the Ti/TiN barrier deposited with the arced magnetron of theinvention and a tungsten plug deposited by chemical vapor deposition(CVD) into the barrier-coated hole. This combination has presented someproblems in the past because tungsten CVD typically uses tungstenhexafluoride (WF₆) as the gaseous precursor. WF₆ tends to attack Ti andto result in structures formed in the W plug resembling volcanoes, whichproduces voids in the plug.

In the first series of tests, the barrier layer consisted of 30 nm of Ticovered by 30 nm of TiN deposited with the arced magnetron of theinvention in an otherwise conventional non-inductive sputter reactor.Following the Ti/TiN deposition, the chip was subjected to rapid thermalprocessing (RTP) in which intense radiant lamps quickly heat the wafersurface for a short period. In the second series of tests, the barrierlayer consisted of 30 nm of Ti covered by 10 nm of TiN deposited as inthe first series. However, in the second test, before the Ti/TiNdeposition the wafer was subjected to a plasma preclean, but there wasno RTP afterwards. In either case, tungsten was then CVD deposited overthe Ti/TiN.

These experiments show that neither process produces volcanoes.Furthermore, thickness and resistivity of the TiN show good uniformity.The TiN resistivity is measured to be less than 45 μΩ-cm. Bottomcoverage of 20% for the TiN/Ti bilayer is observed in holes havingaspect ratios of 5:1 without the use of wafer biasing. Wafer biasingproduces the same bottom coverage in holes having aspect ratios of 10:1.Thus, the Ti/TiN process performed with the magnetron of the inventioncan be successfully integrated into a tungsten plug process. Theinventive magnetron can also be used to sputter deposit other materials,for example, W, using a tungsten target, or TaN, using a tantalum targetand nitrogen gas in the plasma. Reactive sputtering of WN is alsocontemplated.

The magnetron of the invention is thus efficient in producing a highionization fraction because of the high-density plasma it can createwithout excessive power being required. Nonetheless, its full coverageallows for uniform deposition and full target utilization. Itssputtering uniformity is good. Nonetheless, no complex mechanisms arerequired.

The effectiveness of the magnetron of the invention in providinghigh-performance full-coverage sputtering is based on three interrelatedsynergetic effects. The magnetron has a small magnetic area. Thereby,the average magnetic field can be made high, and the plasma lossesreduced. The small magnetron also allows a high average power density tobe applied to the area of the target beneath the magnetron. That is,although the electrical power applied to the target as a whole isrelatively modest, the electrical power density and resulting plasmadensity in the area actually being sputtered at any instant is high. Theasymmetry of the inner and outer magnetic poles of the magnetronproduces portions of the magnetic field extending vertically surroundingthe periphery of the magnetron and extending far into the chamber. Thismagnetic field distribution reduces plasma losses and guides ionizedsputtered particles to the substrate. All of these advantages areenjoyed in a magnetron providing full coverage sputtering of the targetwith only circumferential scanning, and in a magnetron that can beoptimally shaped to produce uniform target sputtering and uniformsubstrate deposition.

Such a small, high-field magnet enables sustained self-sputtering withrelatively modest target power and also enables sputtering of materialssuch as aluminum and titanium at reduced pressures below 0.5 milliTorr,preferably below 0.2 milliTorr, and even at 0.1 milliTorr. At thesepressures, deep hole filling can be facilitated by the reducedscattering of sputtered particles, whether neutral or ionized, and bythe reduced neutralization of ionized particles. However, at least fortitanium, it has been found that with the use of the magnetron of theinvention, deposition rate and bottom coverage are improved with workinggas pressures above 0.7 milliTorr. The high-field magnet furtherpromotes a high ionization fraction, which can be drawn into a deep,narrow hole by biasing of the wafer within proper ranges.

All of these advantages are obtainable in a conventional capacitivelycoupled DC sputter reactor using a magnetron of fairly simple design. Ofcourse, the magnetron of the invention can also be advantageously usedin other types of sputter reactors, such as an HDP reactor relying uponinductively coupled RF power.

What is claimed is:
 1. A magnetron assembly positionable at a backsideof a sputtering target and rotatable about a center position of saidtarget, comprising a single magnetron asymmetrically disposed about saidcenter position and including: a first pole of a first magnetic polaritycomprising a closed band having a central aperture and extending fromsaid center position of said target across a first distance toward acircumferential periphery of said target, wherein said first pole has anoval outer shape with a major axis extending along a radius of saidtarget and wherein said oval shape is egg shaped with a minor axisthereof positioned outwardly of half of said target radius.
 2. Amagnetron assembly positionable at a backside of a sputtering target androtatable about a center position of said target, comprising a singlemagnetron asymmetrically disposed about said center position andincluding: a first pole of a first magnetic polarity comprising a closedband having a central aperture and extending from said center positionof said target across a first distance toward a circumferentialperiphery of said target; and a second pole of a second magneticpolarity disposed in said aperture and separated from said first pole bya gap extending along a surface of said target; wherein said outer poleencloses first area divided into an inner area closer to said centerposition than half of said first distance and an outer area further fromsaid center position than half of said first distance, wherein saidouter area is greater than said inner area and wherein said first polecreates a total magnetic flux at least 50% greater than that created bysaid second pole.
 3. The magnetron assembly of claim 2, wherein saidfirst pole creates a total magnetic flux at least twice that created bysaid second pole.
 4. A magnetron assembly positionable at a backside ofa sputtering target and rotatable about a center position of saidtarget, comprising a single magnetron asymmetrically disposed about saidcenter position and including: a first pole of a first magnetic polaritycomprising a closed band extending a first distance from said centerposition of said target toward a circumferential periphery of saidtarget and having two opposed straight portions extending substantiallyparallel to said radius of said target and disposed asymmetrically withrespect to said center position; a second pole of a second magneticpolarity opposite said first magnetic polarity disposed in said apertureand separated from said first pole by a gap extending along a surface ofsaid target; and a first plurality of magnets of a first magneticstrength disposed as part of said first pole; and a second plurality ofmagnets of a second magnetic strength greater than said first magneticstrength disposed as part of said second pole.
 5. The magnetron assemblyof claim 4, wherein a total magnetic flux of said first plurality ofmagnets is greater than a total magnetic flux of said second pluralityof magnets.
 6. A magnetron assembly positionable at a backside of asputtering target and rotatable about a center position of said target,comprising: a first pole of a first magnetic polarity, producing a firstvalue of a total magnetic flux, and comprising a closed band having acentral aperture extending a first distance from said center position ofsaid target toward a circumferential periphery of said target; and asecond pole of a second magnetic polarity opposite said first magneticpolarity, producing a second value of a total magnetic flux, disposed insaid aperture, and separated from said first pole by a gap extendingalong a surface of said target; wherein a ratio of said first value tosaid second value is at least 1.5.
 7. The magnetron assembly of claim 6,wherein said ratio is at least
 2. 8. The magnetron assembly of claim 6,wherein a width of said first pole at a second distance, equal to halfsaid first distance, from said center position is less than said firstdistance.
 9. A triangularly shaped magnetron, comprising: a triangularlyshaped inner pole face; a plurality of first magnets of a first magneticpolarity disposed in an hexagonal close-packed arrangement adjacent to aplanar side of said inner pole face; a generally triangularly shapedouter pole face surrounding said inner pole face and having twosubstantially straight sides meeting at an apex and a third side joinedto ends of said straight sides opposite said apex; and a plurality ofsecond magnets of a second magnetic polarity disposed in a closed pathalong and adjacent to a planar side of said outer pole face.
 10. Thetriangular magnetron of claim 9, wherein said third side has an arcuateshape concave with respect to said apex.
 11. The triangular magnetron ofclaim 9, wherein said first magnets have a first magnetic strength andwherein said second magnets comprise third magnets having said firstmagnetic strength and disposed along said third side and fourth magnetshaving a second magnetic strength less than said first magnetic strengthand disposed along said straight sides.
 12. A plasma sputtering reactor,comprising: a vacuum chamber; a pedestal for supporting a substratewithin said chamber; a sputtering target in opposition to said pedestaland adapted to be electrically coupled for plasma sputtering; and amagnetron disposed on a side of said target opposite said pedestal andincluding an outer pole face of a first magnetic polarity andsurrounding an inner pole face of a second magnetic polarity oppositesaid first magnetic polarity and a rotation shaft for rotating saidmagnetron about a center position of said target; wherein said outerpole face encloses a first area divided into an inner area closer tosaid center position than half of a first distance extending from saidcenter position of said target to an outer periphery of said target andan outer area further from said center position of said target than halfof said first distance; and wherein said outer pole face has an eggshape with a minor axis located closer to said periphery of said targetthan said center position thereof.
 13. The reactor of claim 12, whereina periphery of said outer pole face is smaller than a periphery of acircle extending from said center position to a portion of said outerpole face furthest removed from said center position.
 14. The reactor ofclaim 12, wherein said outer pole face, said gap, and said inner poleface have oval shapes.
 15. The reactor of claim 12, further comprising aDC power supply of at least 18 kW connectable to said target.
 16. Aplasma sputtering reactor comprising: a vacuum chamber; a pedestal forsupporting a substrate within said chamber; a sputtering target inopposition to said pedestal and adapted to be electrically coupled forplasma sputtering; and a magnetron disposed on a side of said targetopposite said pedestal and including an outer pole face of a firstmagnetic polarity and surrounding an inner pole face of a secondmagnetic polarity opposite said first magnetic polarity and a rotationshaft for rotating said magnetron about a center position of saidtarget; wherein said outer pole face encloses a first area divided intoan inner area closer to said center position than half of a firstdistance extending from said center position of said target to an outerperiphery of said target and an outer area further from said centerposition of said target than half of said first distance, wherein saidouter pole face creates a total magnetic flux at least 50% larger thanthat created by said inner pole face.
 17. The reactor of claim 16,further comprising a DC power supply of at least 18 kW connectable tosaid target.
 18. A plasma sputtering reactor, comprising: a vacuumchamber; a pedestal for supporting a substrate within said chamber; asputtering target in opposition to said pedestal and adapted to beelectrically coupled for plasma sputtering; and a magnetron disposed ona side of said target opposite said pedestal and including an outer poleface of one magnetic polarity producing a total magnetic flux of a firstvalue, surrounding an inner pole face of another magnetic polarityproducing a total magnetic flux of a second value, and a rotation shaftfor rotating said magnetron about a center of said target; wherein aratio of said first value to said second value is at least 1.5.
 19. Thereactor of claim 18, wherein said ratio is at least
 2. 20. The reactorof claim 18, wherein said outer pole face extends from said center ofsaid target to a peripheral portion of said target and has an areasmaller than a similarly extending circle.
 21. The reactor of claim 20,further comprising a DC power supply of at least 18 kW connectable tosaid target.
 22. The reactor of claim 18, further comprising a DC powersupply of at least 18 kW connectable to said target.
 23. The reactor ofclaim 18, further comprising: a DC power supply connectable to saidtarget; an induction coil coupled into an interior of said chamber; andan RF power source connectable to said induction coil.
 24. A magnetronassembly positionable at a backside of a sputtering target and rotatableabout a center position of said target, comprising a single magnetronasymmetrically disposed about said center position aid including: anouter pole of a first magnetic polarity arranged along a closed bandhaving a central aperture and extending from an inner point of saidtarget across a first distance toward a circumferential periphery ofsaid target; and an inner pole of a second magnetic polarity disposed insaid aperture and separated from said outer pole by a gap extendingalong a surface of said target; wherein said outer pole creates a totalmagnetic flux at least 50% greater than that created by said inner pole.25. The magnetron assembly of claim 24, wherein said outer pole enclosesa first area divided into an inner area closer to said center positionthan half of said first distance and an outer area further from saidcenter position than half of said first distance, wherein said outerarea is greater than said inner area.
 26. The magnetron assembly ofclaim 24, wherein said outer pole is arranged in a triangular shape. 27.The magnetron assembly of claim 26, wherein said triangular shape has anarc shape of a side of said triangular shape adjacent to said peripheryof said target.
 28. The magnetron assembly of claim 26, wherein saidinner point is within 20% of a radius of a usable area of said targetfrom said center position.
 29. The magnetron assembly of claim 28,wherein said outer pole overlies said center position of said target.30. The magnetron assembly of claim 26, wherein said outer pole has twoopposed parallel straight sides.
 31. The magnetron assembly of claim 24,wherein said inner point is within 20% of a radius of a usable area ofsaid target from said center position.
 32. The magnetron assembly ofclaim 31, wherein said outer pole overlies said center position of saidtarget.